Data from: Salinity-induced phenotypic plasticity in threespine stickleback sperm activation

Phenotypic expression may be and often is influenced by an organism’s
developmental environment, referred to as phenotypic plasticity. The sperm
cells of teleosts have been found to be inactive in the seminal plasma and
are activated by osmotic shock for most fish species, through release in
either hypertonic (for marine fish) or hypotonic (for freshwater fish)
water. If this is the case, the regulatory system of sperm mobility should
be reversed in salt and freshwater fish. We tested this hypothesis by
first activating sperm of saltwater and freshwater populations of
threespine stickleback in salt- and fresh water. The sperm from saltwater
stickleback could be activated in either salinity, which matches the
freshwater colonization history of the species, whereas the sperm from the
freshwater population acted as predicted by the osmotic shock theory and
was activated in freshwater only. As the freshwater population used here
was calculated to be thousands of years old, we went on to test whether
the trait(s) were plastic and sperm from freshwater males still could be
activated in saltwater after individuals were exposed to saltwater. After
raising freshwater stickleback in saltwater we found the mature males to
have active sperm in both salt and freshwater. Further, we also found the
sperm of wild-caught freshwater stickleback to be active in saltwater
after exposing those mature males to saltwater for only two days. This
illustrates that the ability for stickleback sperm to be activated in a
range of water qualities is an environmentally induced plastic trait.